1. Field of Industrial Applications
This invention relates to a method for producing silicon nitride ceramics of a complex shape by reactive sintering.
2. Prior Art
Silicon nitride and silicon carbide are finding more uses as a structural material owing to their superior heat resistance and corrosion resistance. However, because of their poor moldability, it is hard to manufacture an article having a complex shape. Therefore, in order to obtain a complex shaped article from silicon nitride and silicon carbide, it has to bond molded parts being simply shaped.
For achieving such bonding, several methods have been proposed such as bonding by a hot press, bonding with a bonding agent, and bonding by mechanical engagement. These bonding methods require complicated steps and results in high production cost. Moreover, they have drawback that the joints are weaker than the parent material. In the case of silicon nitride or silicon carbide, that is, non-oxide ceramics material, an adhesive like an alumina-based or silica-based adhesive that has been used for preparing oxide ceramics cannot be easily applied, because said non-oxide ceramics have a strong tendency toward covalent bonding and consequently are poor in wetting and reactivity with a molten material.
A silicon nitride sintered body of a complex shape may be considered to produce by bonding molded items made up mainly of silicon powder with a solvent-containing adhesive composed mainly of silicon powder, and then heating the assembly in a nitriding atmosphere. This method should provide a silicon nitride sintered body firmly bonded with a continuous joint phase of silicon nitride. In actual, however, the use of a solvent-containing adhesive causes cracking because the solvent infiltrates into the moldings to swell them.